One thing which always annoyed me about Photoshop was a part of the layer styles. As a Photoshop user, you will know you can add certain styles to certain layers. However if you wanted to copy a layer style to another layer, it'd overwrite that layers current style too.
A hidden gem in Photoshop which isn't actually shown anywhere on the GUI is the ability to paste a layer style without it overwriting the layers current style. It's in the form of a hotkey - ctrl + alt + cmd + V